1. Field of the Invention
The present invention relates to a touch panel. In particular, this invention relates to a device for improving the accuracy of the touch point on a touch panel and a method thereof.
2. Description of the Related Art
Traditionally, the input of an electronic device is implemented by a keyboard or a mouse. However now touch panels are extensively applied to a variety of electronic devices, the user can use fingers or touch pens to click the touch panel to input data to the electronic devices. A sensor located below the touch panel senses the touch point's location to operate the electronic device. According to the detection mechanism for sensing the touch point's location, the touch panel can be divided into a resistive type, a capacitive type, an acoustic wave type, an optical type, and an electromagnetic type. According to the kind of the touch panel, the touch panel can be divided into a touch panel and a touch pad.
For a capacitive touch panel that uses the capacitive type touch detection mechanism, it detects the currents from each sides of the touch point and uses the currents to determine the touch point's location.
Reference is made to FIG. 1, which shows a schematic diagram for detecting the touch point location on the capacitive touch panel in the prior art. The capacitive touch panel 10 is composed of a transparent substrate layer 11, a conductive metallization layer 12, an electrode pattern layer 13, and an insulation hard plating layer 14. The transparent substrate layer 11 can be a glass. The electrode pattern layer 13 is formed on the edge of the touch panel 10 for compensating the electric field distribution above the conductive metallization layer 12. Furthermore, when viewed in conjunction with FIG. 2, each of the four corners of the touch panel 10 is connected with each of external conducting wires A, B, C, D for receiving each of the AC detection signals, AC1, AC2, AC3, and AC4 that are used for determining the touch point location P on the touch panel 10.
The AC detection signals, AC1, AC2, AC3, and AC4, are AC square wave voltage signals or AC sine wave voltage signals, and their amplitude are the same as each other. At this time, each of currents I1, I2, I3, I4 respectively flows through each of the external conducting wires A, B, C, and D. By measuring the current variations ΔI1, ΔI2, ΔI3 and ΔI4 at the external conducting wires A, B, C, D of before the user touches the touch point P and of when the user touches the touch point P, the coordinates of the touch point P can be calculated by the following formulas.x=(ΔI3+ΔI4−ΔI1−ΔI2)/(ΔI1+ΔI2+ΔI3+ΔI4)  (1)y=(ΔI1+ΔI4−ΔI3−ΔI2)/(ΔI1+ΔI2+ΔI3+ΔI4)  (2)
However, if the touch panel 10 does not have the electrode pattern 13, the distribution of the electric filed of the AC detection signals, AC1, AC2, AC3, and AC4 on the touch panel 10 would be curved, as shown in FIG. 3. The electric filed distribution curve in FIG. 3 forms equipotential lines in FIG. 4. The location of the touch point P would be inaccurate. For overcoming the above problem, a compensation means is applied to the touch panel, such as summing the electrode pattern layer 13 at the four corners of the touch panel 10. The equipotential lines are thereby improved, as shown in FIG. 5, and become linear.